1. Field of the Invention
The present invention relates generally to identification plates for transmitting and receiving data using electromagnetic waves, and in particular, to an identification plate with a damping element for limiting a reading range of the identification plate.
2. Description of the Related Art
An identification plate is characterized by a data carrier having an electronic chip which can be read remotely by a reading device, and optionally written as well. The energy required for the operation of the chip is received wirelessly from the reading device. Both data and energy are transmitted via an electromagnetic field.
Identification plates for the purpose of identifying a person are commonly the size of a credit card. In the case of identification plates having an operating frequency in the UHF range (865-868 MHz) and the SHF range (2446-2454 MHz), it is possible to implement lambda-half dipole antennas, or at least dipole antennas which are mechanically truncated but electrically extended. This construction enables a range of several meters. This range also makes it possible to identify persons in a motor vehicle, thereby also indirectly enabling access control for the motor vehicle used by the identified person.
It has been demonstrated that the range between an identification plate and a reading device can be dependent on the type of motor vehicle. In addition, this occurrence has been traced back to, among other things, a layer of insulation in the windshield which insulates against both temperature and light, and which also simultaneously acts to dampen electromagnetic waves. Although every windshield which includes an insulation layer has a window which is transparent to electromagnetic waves, the fact that the reading range depends on the type of motor vehicle persists.
Instead of this state of affairs, it would be desirable for the reading range to be consistent across different vehicles. In order to enable a reliable reading of an identification plate located in the interior of a motor vehicle with a strong damping effect, the sensitivity of the reading device would have to be designed for and adjusted to a strong damping effect. In the case of vehicles with a very low damping effect, however, a very large range would result, and this can lead to interference. For example, where there are multiple road lanes with lifting gates, it may be possible that the reading device assigned to the selected road lane is not the only one activated, but rather additional neighboring reading devices are also activated. This would be undesirable. Accordingly, the reading range would need to be reduced for vehicles with a very low damping effect, by suitable means.